They appoint three board members between them, matching the government's quota.
A final three, also chosen by the government, must be from outside politics. For a 4G project to get FDN financing, the board must sign it off.
The hope is that the foreign and independent members will reject those that show signs of rigged bids or padded contracts.
So far the model appears to be working well.
By the end of 2018 the FDN expects to have closed financing for 17 projects, worth $8.4bn, of the 30 planned under the 4G banner.
Of that, 24% will come from abroad. It is now branching out from roads to other investments, including Bogotá's Metro,
which will be Colombia's priciest infrastructure project to date, at an estimated cost of $ 4.6bn for 25km of elevated track.
The bank will soon need more capital. In 2016 the Colombian government sold its stake in Isagen, a power-generating company,
to a Canadian investment fund for $ 2bn, and used the money to buy FDN bonds, giving the institution the wherewithal to fund its endeavours.
But to continue long-term infrastructure financing, says Mr Valle, an IPO will soon be needed.
A bigger problem, says Mario Dib, who manages one of the infrastructure-debt funds set up by the FDN, is that Colombians hate road tolls.
Earlier this year tolls were suspended in Urabá, in the country's north, after protesters burnt toll-points and killed three people.
The government has agreed to pay FDN concessionaires any money they are unable to collect.
That is supposed to give investors the certainty they need to keep coming.
But it would weaken the rationale for the FDN if taxpayers are stuck with bills they were never supposed to pay.
And it raises fears that a future government might sour on the institution.
The next presidential election, in 2022, coincides with the expected completion of many 4G roads.
If the tolls spark more protests, and someone less market friendly than the centre-right incumbent, Iván Duque, wins,
public-private partnerships might fall out of fashion. That would be rotten luck for those trying to fix Colombia's rotten infrastructure.